Ethylene and propylene are two basic raw materials with the largest consumption and many applications in chemical industry and are referred to as the stem of the modern organic synthesis industry, and therefore the production technology thereof is the emphasis to be developed competitively by the developed countries. The main route of producing the two olefins is light oil cracking and other methods include the catalytic conversion of lower alcohol ethers, aldehydes, mercaptans, and halohydrocarbons. The impacts of twice petroleum crises in 1970s accelerated the research and developing work of the technology for producing lower olefins through a non-petroleum raw material route wherein the process of methanol conversion has been developed rapidly and shows an enormous commercial application perspective.
Firstly, a process technology for producing lower olefins by taking ZSM-5 zeolite as catalyst and methanol as raw material was provided by Mobile Co., US.
Thereafter, in the middle of 1980s, an assumption of producing lower olefins with a catalyst of a non-zeolite type heteroatom containing aluminum phosphate salt molecular sieve was proposed by Union Carbide Corporation of USA (U.S. Pat. No. 4,499,327).
In 1990, a result of the conversion of methanol to lower olefins high selectively with a catalyst of a SAPO-34 type silicoaluminophosphate molecular sieve having a micropore structure of chabasite was published by Dalian Institute of Chemical Physics, Chinese Academy of Sciences for the first time (Applied Catalysis, 1990, Volume 64, P31-40). Subsequently, a new technology for synthesizing SAPO-34 molecular sieve, a preparation technology of SAPO-34 molecular sieve catalysts and a process technology for producing lower olefins from methanol or/and dimethyl ether were proposed (the patent numbers are CN1037334C, CN1038125C, CN1048429C, CN1065853C, CN1067603C and CN1076219C, respectively), and therefore the production costs of SAPO-34 molecular sieve and the catalyst thereof were reduced substantially, the yields of ethylene and propylene were increased prominently and the economic competitive power of the process technology approached to the level of the petroleum cracking technology.
As stepping into the 21st century, in order to cope with the great pressure of scarce petroleum resources and the rapidly increasing oil price, the process technology for producing lower olefins from methanol or/and dimethyl ether using SAPO-34 molecular sieve catalyst developed by the applicant has been capable of satisfying the demand of industrial implementation.
Due to the small pore characteristic of SAPO-34 molecular sieve, this solid acid catalyst tends to be coked quickly and deactivated temporarily in an organic reaction and can be used only after a regeneration by carbon burning. In a continuous industrial production, the continuous stable operation of the small pore molecular sieve such as SAPO-34 or the like can be ensured only when a circulating fluidized apparatus including a reactor and a regenerator is used. In the fluidized apparatus, the temperature of the bed of the reactor for the conversion of methanol or/and dimethyl ether to lower olefins is 400 to 550° C. and the temperature of the catalyst bed of the regenerator is 550 to 700° C. The circulating fluidized apparatus have a very common application in the process of petroleum fluid catalytic cracking (FCC). These apparatus have no heating components themselves and at the stage of starting up, the temperatures of the apparatus are increased depending by the external auxiliary heat-supplying equipment's. In industry, such fluidized apparatus is very large in size and the filled catalyst at starting up is up to hundreds of tons, therefore very large amount of heat is needed to increase the bed temperatures of the reactor and the regenerator of the apparatus to 500° C. or above, and especially when it is over 400° C. or above, it is very difficult to increase the temperature by utilizing external heat.
A method commonly used in the process of FCC is that when the temperature of the regenerator catalyst bed attains 370° C. or above, diesel fuel is spray into the bed and the temperature of the apparatus is elevated using the combustion exothermic reaction of the diesel fuel. The advantage of this method is that it can increase the temperature of the apparatus rapidly and reduce the starting up time greatly. At the same time, FCC is an endothermic reaction and the catalyst is needed to carry heat from the regenerator to maintain the temperature of the catalyst bed, therefore in the actual operation, fuel oil should be sprayed to the regenerator continuously to maintain the temperature of the regenerator.
However, this method has the following disadvantages: (1) a mass of diesel oil is consumed additionally; (2) at the initial stage of spraying oil, as the diesel fuel cannot be burn completely, a mass of carbon black is produced and covered on the catalyst surface, and a part of the carbon black is flowed into the atmosphere with the tail gas and causes pollution to a certain extent; and (3) local superheating may occur so as to make the activity of part of catalyst lost permanently. As the process of the conversion of methanol or/and dimethyl ether to lower olefins is a strong exothermal reaction and the fluidized process of producing lower olefins from methanol or/and dimethyl ether has no precedents in industrial implement, especially SAPO-34 molecular sieve catalyst has not passed the test of actual industrial operation, whether the heating up method of spraying oil in FCC process is feasible or not is still unknown.
Therefore, how to utilize the characteristics of conversion reaction and start up the process is a challenge for this process in industrial implement.